A band mill is conventionally used as an apparatus for cutting a large metal workpiece. In a band saw blade used for the band mill, in order to cope with chatter vibration or noise, a pattern of set teeth is set to various set patterns such as raker set, wave set and straight set, and pitch between the teeth is made non-uniform. In order to cope with difficult-to-machine material such as stainless steel, there is developed a saw blade in which a plurality of teeth of the saw blade are varied in height or the set amount of the plurality of set teeth is varied.
To meet commercial requirements, there have been developed various saw blades such as a saw blade in which angles of tips of saw teeth are variously changed, a back surface of the saw blade is corrugated, or a curve line connecting tips of the teeth of the saw blade is corrugated.
Concerning also a band mill which cuts a metal workpiece for example, various band mills have been developed in accordance with usage of cutting operations. For example, cutting methods of the band mills are roughly divided. There are two kinds of methods, i.e., (1) a case in which a cutting speed is constant irrespective of a cutting length of a workpiece, and (2) a case in which the cutting speed is variable in accordance with the cutting length of a workpiece.
The methods (2) in which the cutting speed is variable in accordance with the cutting length of a workpiece can further be divided into
(2-1) a method for controlling back pressure generated in a cylinder using a hydraulic cylinder,
(2-2) a method for controlling a flow rate in accordance with cutting resistance using a hydraulic cylinder,
(2-3) a CNC controlling method in which a shape of a workpiece is previously input, the cutting length of a workpiece is calculated each time and the cutting speed is changed,
(2-4) a CNC controlling method in which a cutting resistance is detected, and the cutting speed is changed in accordance with the cutting resistance, and
(2-5) a weight of a housing to which the saw blade is mounted is mechanically adjusted and restrained, and a workpiece is cut by free fall.
Conventionally, band mills such as a small and inexpensive portable band saws are widely used. Generally, the small portable band saw, a lateral type band saw are of the hinge type in which a saw blade housing is vertically swung such as to draw an arc, and the method of (2-5) is frequently used. Such a band mill is called “light-load saw mill” herein after in this specification.
The light-load sawmills in the common market are suitable for cutting a relatively small workpiece in a cutting operation on a building site of steel construction. Although such workpiece shapes are limited to small objects, the kinds of the workpiece shapes vary widely, and cutting operations of workpieces such as different shaped steels, pipes and small-diameter solid materials are carried out.
In the light-load saw mills as described above, as shown in FIGS. 1A and 1B, one set pattern comprises three teeth, i.e., one spur tooth S and a pair of left and right set tooth L and R having a constant set amount in the lateral direction, and this set pattern is repeated. When a solid material W having a diameter of 50 mm is cut using a saw blade 101 having a pitch of 4 mm as shown in FIG. 3, an appropriate cutting operation can be carried out. When a pipe material P having a diameter of 50 mm and a thickness of 3 mm is cut using the same saw blade 101 as shown in FIG. 4, however, there is a problem that the saw blade 101 is prone to be broken off.
This is because that although the pitch of the saw blade 101 is 4 mm, the thickness of the pipe material P is 3 mm and the cutting speed of the saw blade 101 is close to a free fall of a housing load G and thus, if the cutting operation by the saw blade 101 reaches near the center of the pipe material P in this cutting condition, the workpiece P enters between a tip and a tip of the saw blade 101, and abrupt free fall is generated, a cutting amount becomes excessively increased and thus, the teeth are prone to be broken.
As a current method for solving this problem, as shown in FIGS. 2A and 2B, it is common to cut a pipe material P using a saw blade 103 having a pitch smaller than a thickness of the pipe material P. FIG. 5 shows a state in which a pipe material P having a thickness of 3 mm and a diameter of 50 mm is cut using a saw blade 103 (saw blade shown in FIGS. 2A and 2B) having a pitch of 2 mm.
Under this condition, since the pitch of the saw blade 103 is as small as 2 mm with respect to the 3 mm thickness of the pipe material P, even if the saw blade 103 reaches near the center of the pipe material, the workpiece P does not enter between a tip and a tip of the saw blade 103, and abrupt free fall is not generated, an appropriate cutting operation is carried out.
If a solid material W (workpiece shown in FIG. 3) having a diameter of 50 mm is cut using the same saw blade 103, i.e., the saw blade 103 (saw blade shown in FIGS. 2A and 2B) having the pitch of 2 mm, however, since the pitch of the saw blade 103 is sufficiently smaller than the diameter of the workpiece W, abrupt free fall is not generated and the excessive cutting is not generated. However, the number of teeth of the saw blade 103 acting on a cutting length of the workpiece W is large, and a cutting amount of each tooth with respect to the workpiece W becomes small. Therefore, there is a problem that the cutting time becomes long as compared with a case in which a solid material W is cut by the saw blade 101 having the pitch of 4 mm.
For the above-described reason, when a workpiece such as a solid material and a pipe material is cut, there is a problem that it is necessary to exchange saw blades having an appropriate pitch in accordance with shape and size of the workpiece P and it takes time and labor for exchanging the saw blades.
Therefore, various workpieces are cut on building site and the like, and labor for exchanging saw blades having different pitches in accordance with shape and size of workpieces is not negligible. Even if a saw blade having relatively small pitch is previously mounted for the sake of preventing the teeth from being broken, if a workpiece having relatively long cutting length, a problem in which the cutting time becomes long is not negligible.
The present invention has been accomplished to solve the above problems, and it is an object of the invention to provide a saw blade capable of efficiently cutting workpieces having relatively long or small cutting length while preventing the teeth from being broken.